Fix WSGI error handling
    
    A number of different errors could occur when trying to handle an
    error which just confused matters.
    
    If no CCache was received then trying to retrieve context.principal
    in the error message caused yet another exception to be raised.
    
    Trying to get Command[name] if name wasn't defined in command would
    raise an exception.
    
    Trying to raise errors.CCache was failing because the response hadn't
    been started.
    
    https://fedorahosted.org/freeipa/ticket/2371